Electrical Power Systems

334 Electrical Power Systems
New load in area-1 and area-2,
Generation in area-1 and area-2,
LOAD 1 = 20,000 – 1000 + 17.392 = 19017.392 MW
LOAD 2 = 40,000 + 36.616 = 40036.616 MW
PG 1 = 19000 – 305.13 = 18694.87 MW
PG 2 = 41000 – 640.78 = 40359.22 MW
P tie,21 = LOAD 1 – PG 1 = 19017.392 – 18694.87
\ P tie,21 = 322.522 MW.
(b) With supplementary control
(i) Loss of 1000 MW load in area-1
Area-1 has a generating capacity of 4000 MW on supplementary control and this will reduce
generation so as to bring ACE 1 to zero. Similary, area-2 generation on supplementary control
will keep ACE 2 at zero.
ACE 1 = B 1 Df + DP tie,12 = 0
ACE 2 = B 2 Df – DP tie,12 = 0
Hence, Df = 0.0, DP tie,12 = 0.0
Area-1 generation and load are reduced by 1000 MW. There is no steady-state change in
area-2 generation and load, or the tie flow.
(ii) Loss of 500 MW generation carrying part of spinning reserve in area-1:
Spinning reserve lost with generation loss is
500 ´ 1000
= 166.67 MW
b4000 - 1000g
Spinning reserve remaining is (1000 – 166.67) = 833.33 MW. This is sufficient to make up
500 MW. Hence, the generation and load in the two areas are restored to their pre-disturbance
values. There are no changes in system frequency or tie-line power flow.
12.19 GENERATION RATE CONSTRAINT (GRC)
In establishing AGC signals, it should be recognized that there is a limit to the rate at which
generating unit outputs can be changed. This is particularly true for thermal units where
mechanical and thermal stresses are the limiting factors. igure 12.24 shows the flow chart for
incorporating the effect of GRC in the matrix differential equation X • = AX + BU + Gp for
obtaining the system response at various states. At each time interval of Dt seconds for
integration, the generation rate is checked for its magnitude and sign; that is for the K-th
•
interval, if the generation rate | DP gi,k | are less than or equal to a specified maximum rate
(say r), the corresponding generation changes DPgi,k is not altered. In case the generation rate
exceeds the maximum specified rate r, the generation change is constrained through the
relationship
DP gi,k = DP gi,k-1 + r.Dt ...(12.49)